Americans have been killed by prisoners released from the detention center at Guantanamo Bay, Cuba, a senior Defense Department official told lawmakers Wednesday, triggering sharp criticism from Republicans opposed to shuttering the facility in the wake of deadly attacks by the Islamic State group in Brussels and Paris.

Paul Lewis, the Pentagon's special envoy for Guantanamo detention closure, declined to provide the GOP-led House Foreign Affairs Committee with details. He would not say whether the incidents occurred before or after President Barack Obama took office in January 2009.

"What I can tell you is unfortunately there have been Americans that have died because of (Guantanamo) detainees," Lewis said during an exchange with Rep. Dana Rohrabacher, R-Calif.

"When anybody dies, it is tragedy and we don't want anybody to die because we transfer detainees," Lewis said.

An Obama administration official said Lewis was referring to an incident that involved an Afghan prisoner released from Guantanamo while George W. Bush was president. The official was not authorized to speak publicly and requested anonymity.

During the Bush administration, 532 prisoners were released from Guantanamo, often in large groups to Afghanistan and Saudi Arabia — the two nationalities that made up the greatest number of prisoners.

The Obama administration has released 144 detainees after a screening process that involves representatives from six government agencies and departments who must make a unanimous decision to release.

Lewis testified before the committee along with Lee Wolosky, the State Department's special envoy for Guantanamo closure. They argued the prison is a powerful propaganda tool for the Islamic State group and keeping it open damages U.S. national security.

Republicans and a few Democrats in Congress have repeatedly thwarted Obama's effort to close the prison and blocked any attempt to move detainees to U.S. prisons in legislation the president has signed into law.

Wolosky said the Guantanamo prison did not prevent Tuesday's attacks in Brussels that killed at least 34 people and wounded more than 200 or the November 13 attacks in Paris.

"There are unfortunately going to be acts of terrorism, probably whether the facility is opened or closed," Wolosky said. "The proper analysis is, 'What are the risks of keeping it open in light of the very obvious use of that facility as a propaganda tool,' which, frankly, you should not have to question."

The committee's hearing marked the first open exchange between the Obama administration and Congress over the utility and future of the prison since Obama sent his plan for shutting it down to Capitol Hill last month. The proposal was greeted with firm opposition from Republicans, who declared his proposal to deliver an unfulfilled campaign promise a non-starter.

Republicans see the prison at Guantanamo as more essential than ever. With the Islamic State group carrying out deadly assaults in Europe and expanding its base in Libya, they said, there needs to be a place to hold terrorist suspects. Republicans have refused Obama's request that Congress change the law that prohibits moving detainees accused of violent extremist acts to U.S. soil.

The committee's chairman, Rep. Ed Royce of California, and other GOP lawmakers have also criticized the Obama administration for moving detainees to countries that are probably unable to ensure they don't resume the behaviors that got them locked up in the first place.

"Countries like Ghana and Uruguay aren't typical security and intelligence partners, but they are being asked to shoulder a heavy burden and responsibility," Royce said.

There are 91 men held at Guantanamo, down from nearly 250 when Obama assumed the presidency. Those left include 36 who are cleared for release if security conditions can be met in the countries where they will settle. Seven face trial by military commission, including five charged with planning and supporting the terrorist attack of Sept. 11, 2001. Three others have been convicted.

The Director of National Intelligence reported this month that 5 percent of Guantanamo prisoners released since January 2009, when the U.S. began using the multi-agency screening process, have re-engaged in terrorism and 8 percent are suspected of it. That compares to 21 percent confirmed and 14 percent suspected under the earlier system.